Group B streptococci (GBS), or Streptococcus agalactiae, are a major cause of neonatal bacterial infection in the United States (Baker, C. J., and M. S. Edwards, “Group B streptococcal infections,” p. 1091-1156 in J. Remmington and J. O. Klein (ed.), Infectious diseases of the fetus and newborn infants, 5th ed. The W. B. Saunders Co. Philadelphia, Pa. (2001)). GBS are normally colonized in human genital and lower gastrointestinal tracts and can be vertically transmitted from mother to baby during a normal vaginal delivery. Common manifestations of GBS disease in neonates include sepsis, meningitis, pneumonia and joint infections. About 21% of pregnant women are vaginally colonized with GBS and a significant high percentage of babies develop symptoms associated with GBS infection. For example, sepsis occurs in 16 of 1,000 live births to women with GBS colonization, while only in 0.4 of 1,000 live births to women without GBS colonization (Regan, J. A., M. A. Klebanoff, R. P. Nugent & 7 other authors. 1996. Colonization with group B streptococci in pregnancy and adverse outcome. Am. J. Obstet. Gynecol. 174: 1354-1360).
Intrapartum antibiotic prophylaxis (IAP) is the primary prevention suggested by the Centers for Disease Control and Prevention (CDC) because it can effectively reduce neonatal GBS colonization and early-onset infection (Centers for Disease Control and Prevention, “Prevention of perinatal group B streptococcal disease: a public health perspective,” Morbid. Mortal. Weekly Rep. 45: 1-24 (1996); and Centers for Disease Control and Prevention, “Prevention of perinatal group B streptococcal disease: revised guidelines from CDC,” Morbid. Mortal. Weekly Rep. 51: 1-22 (2002)). IAP is usually given to pregnant women colonized with GBS 4 hrs before delivery to prevent vertical transmission. However, there are many places in the world that GBS culture screening is not routine for pregnant women and universal administration of antibiotics may present a potential threat to neonates. Antibiotic resistance is another major concern because some GBS clinical isolates are already found to be resistant to erythromycin and clindamycin (Fernandez, M., M. Hickman, and C. J. Baker, “Antimicrobial susceptibilities of group B streptococci isolated between 1992 and 1996 from patients with bacteremia or meningitis,” Antimicrob. Agents Chemother. 42: 1517-1519 (1998); Centers for Disease Control and Prevention, “Prevention of perinatal group B streptococcal disease: revised guidelines from CDC”, Morbid. Mortal. Weekly Rep. 51: 1-22 (2002)). Thus, there is a need for a direct and effective alternative to IAP.
One promising approach to the detection and treatment of pathogenic bacteria is the use of bacteriophage lytic enzymes as bacteriolytic agents. Bacteriophage lytic enzymes responsible for bacterial host lysis are also known as lysins. Many lysins can rapidly break down the bacterial cell wall in order to release progeny phage (Young, R. 1992. Bacteriophage lysis: mechanism and regulation. Microbiol. Rev. 56:430-481). Structurally, lysins are commonly found as modular proteins with an amino terminal domain that confers the enzymatic activity for a peptidoglycan bond and a carboxy terminal domain that confers binding specificity to a carbohydrate epitope in the bacterial cell wall (Loessner, M., K. Kramer, F. Ebel, and S. Scherer, “C-terminal domains of Listeria monocytogenes bacteriophage murein hydrolases determine specific recognition and high-affinity binding to bacterial cell wall carbohydrates,” (Mol. Microbiol. 44:335-349 (2002); Lopez, R., E. Garcia, P. Garcia, and J. L. Garcia, “The pneumococcal cell wall degrading enzymes: a modular design to create new lysins?,” MicroB. Drug Resist. 3:199-211 (1997); Lopez, R., M. P. Gonzalez, E. Garcia, J. L. Garcia, and P. Garcia, “Biological roles of two new murein hydrolases of Streptococcus pneumoniae representing examples of module shuffling,” Res. Microbiol. 151:437-443 (2002); Sheehan, M. M., J. L. Garcia, R. Lopez, and P. Garcia, “The lytic enzyme of the pnemococcal phage Dp-1: a chimeric enzyme of intergeneric origin,” Mol. Microbiol. 25:717-725 (1997)). Lysins are believed to provide at least one of the following enzymatic activities against a peptidoglycan substrate: muramidases, glucosaminidases, N-acetylmuramyl-L-alanine amidase and endopeptidases (Young, R., “Bacteriophage lysis: mechanism and regulation,” Microbiol. Rev. 56:430-481 (1992)). Purified lysin from a bacteriophage can be applied exogenously to affect bacterial lysis (Loeffler, J. M., D. Nelson, and V. A. Fischetti, “Rapid killing of Streptococcus pneumoniae with a bacteriophage cell wall hydrolase,” Science. 294:2170-2172 (2001); Loessner, M., G. Wendlinger, and S. Scherer, “Heterogeneous endolysins in Listeria monocytogenes bacteriophages: a new class of enzymes and evidence for conserved holin genes within the siphoviral lysis cassettes,” Mol. Microbiol. 16:1231-1241 (1995); Loessner, M., S. K. Maier, H. Daubek-Puza, G. Wendlinger, and S. Scherer, “Three Bacillus cereus bacteriophage endolysins are unrelated but reveal high homology to cell wall hydrolases from different bacilli,” J. Bacteriol. 179:2845-2851 (1997); Nelson, D., L. Loomis, and V. A. Fischetti, “Prevention and elimination of upper respiratory colonization of mice by group A streptococci by using a bacteriophage lytic enzyme,” Prot. Natl. Acad. Sci. USA. 98:4107-4112 (2001)).
Lysins are normally very specific to the bacterial species from which the lysin derived phage was isolated (Fischetti, V. A. 2003. Novel method to control pathogenic bacteria on human mucous membranes. Ann. N.Y. Acad. Sci. 987:207-214; Fischetti, V. A. 2001. Phage antibacterials make a comeback. Nature Biotechnol. 19:734-735). Although the range of bacteria targeted by lysins is less restrictive than the corresponding bacteriophage, lysins still maintain a degree of specificity, having minimal effects on other bacteria including commensal organisms. While bacteriophage host ranges are largely restrictive, recognizing only one specific antigen on its bacterial host, phage lysins are less restrictive, recognizing a specific carbohydrate molecule common to the particular species of host bacteria.
Bacterial resistance to phage lysins is believed to be less likely to arise as compared with bacteriophage adsorption for at least two reasons: first, bacterial lysis upon exposure to lysin is almost immediate, not giving bacteria much possibility for mutation and second, lysins bind to highly conserved molecules in the bacterial cell wall that are under selective pressure not to mutate. In contrast, bacterial resistance to many antibiotics is often easily identified. Furthermore, the problem with lysogenic conversion is reduced or eliminated with phage lysins, and animal testing and treatment can be performed effectively using lysins.
There is an ongoing need for therapies and agents effective in the diagnosis and control of bacterial contamination, colonization and infection. In addition, compounds with bacteriocidal effects may be useful in the decontamination of bacteria on inanimate surfaces and objects. The bactiophage lytic enzymes provided are useful in providing agents useful in the detection or killing of Group B streptococci (GBS) bacteria.